Device for detecting seat occupancy in a motor vehicle

Abstract

A device for detecting seat occupancy in a motor vehicle, especially for inhibiting airbag release when a seat is unoccupied, is provided. A seat occupancy sensor has a front sensing region and a rear sensing region, which can be evaluated separately. In this way, it is possible to determine whether the front seat passenger is in a sitting position close to the front seat edge of the seat cushion, which reduces the protective effect of the airbag. This can possibly be indicated visually or audibly. As a further measure, the inhibiting of an airbag release can be provided in the case of an incorrect sitting position. The seat occupancy sensor can be a resistive membrane pressure sensor.

What is claimed is: 
     
       1. A device for detecting seat occupancy states in a motor vehicle, the device comprising: a seat occupancy sensor integrated in a seat cushion of the seat;   an evaluation circuit coupled to the seat occupancy sensor;   wherein said seat occupancy sensor is divided into a front sensing region and a rear sensing region, said front sensing region responding to seat occupancy in a front region of the seat cushion and the rear sensing region responding to seat occupancy in a rear region of the seat cushion; and   wherein an occupancy state of both said front and rear regions is separately evaluated by said evaluation circuit to control an airbag.   
     
     
       2. A device according to claim 1, wherein when the seat occupancy is detected primarily in the front sensing region, the evaluation circuit emits a warning signal to at least one of an audible and visual warning device. 
     
     
       3. A device according to claim 1, wherein when the seat occupancy is detected primarily in the front sensing region, the evaluation circuit emits a control signal to a release controller for the airbag, said control signal making the release of the airbag more difficult. 
     
     
       4. A device according to claim 1, wherein when the seat occupancy is detected primarily in the rear sensing region, the evaluation circuit emits a control signal which makes a release controller for an airbag ready to release. 
     
     
       5. A device according to claim 1, wherein the evaluation circuit uses signals from the seat occupancy sensor and a longitudinal seat position of the vehicle seat to determine an absolute distance between an occupant and the airbag, and emits a warning signal if said absolute distance is less than a minimum distance. 
     
     
       6. A device according to claim 1, further comprising a non-volatile storage medium coupled to the evaluation circuit, said storage medium storing data which is input, output, or used internally in the evaluation circuit. 
     
     
       7. A device according to claim 6, wherein the storage medium is carried out in accordance with a stacking principle, in which case relatively old data in the storage medium are overwritten cyclically by relatively new data received in the storage medium. 
     
     
       8. A device according to claim 1, wherein the seat occupancy sensor is constructed as a resistive membrane pressure sensor. 
     
     
       9. A device according to claim 8, wherein the membrane pressure sensor is formed from a front pressure sensor and a rear pressure sensor, each of which has a meandering double cable, each double cable being formed from a first conductor track and a second conductor track which runs predominantly parallel thereto. 
     
     
       10. A device according to claim 9, further comprising three connecting contacts, wherein one end of said first conductor track of each of said double cables is connected to respective ones of said three connecting contacts, and another end is connected via respective diodes to a common junction point, wherein said second conductor tracks of said double cables are connected together to form a common cable having one end connected to another one of said three connecting contacts, and another end connected to said common junction point. 
     
     
       11. A device according to claim 1, wherein in addition to an interrogation of the occupancy state, a functional test for both sensing regions is separately carried out by said evaluation circuit. 
     
     
       12. A device according to claim 10, wherein an initial evaluation circuit is connected to the three connecting contacts, and wherein a measurement voltage having alternating polarity is in each case applied to two of said three connecting contacts, and further wherein seat occupancy signals for the front sensing region and for the rear sensing region are determined from the respective measurement currents, and still further wherein an error signal with respect to the operation of the seat occupancy sensor is determined from the respective measurement currents. 
     
     
       13. A device according to claim 1, wherein when the seat occupancy is detected primarily in the front sensing region, the evaluation circuit emits a control signal to a release controller for the airbag, said control signal inhibiting the release of the airbag. 
     
     
       14. A device for detecting seat occupancy states in a motor vehicle, the device comprising: a seat occupancy sensor integrated in a seat cushion of the seat;   an evaluation circuit coupled to the seat occupancy sensor;   wherein said seat occupancy sensor is divided into a front sensing region and a rear sensing region, said front sensing region responding to seat occupancy in a front region of the seat cushion close to a front seat edge, and the rear sensing region responding to seat occupancy in a rear region of the seat cushion; and   wherein an occupancy state of both said front and rear regions is separately evaluated by said evaluation circuit.   
     
     
       15. A device for detecting seat occupancy states in a motor vehicle, the device comprising: a seat occupancy sensor integrated in a seat cushion of the seat;   an evaluation circuit coupled to the seat occupancy sensor;   wherein said seat occupancy sensor is divided into a front sensing region and a rear sensing region, said front sensing region responding to seat occupancy in a front region of the seat cushion close to a front seat edge, and the rear sensing region responding to seat occupancy in a rear region of the seat cushion;   wherein an occupancy state of both said front and rear regions is separately evaluated by said evaluation circuit; and   whereby a response from only said front sensing region indicates an incorrect seat occupancy state for an airbag release.